The present invention relates to a taping unit for cardboard case taping machines with an improved movement for the return of the entry application roller.
The term "taping unit" relates to those automatic machines which execute the application of lengths of adhesive tape on the top and bottom walls (and in part on the leading and trailing vertical ones) of parellelepiped cardboard cases which are made to progress along a predetermined operating path.
In such machines the "taping units" are the particular mechanisms (usually two per machine, or lower and one upper) used for the delivery of the tape and for its adhesion to the case walls.
Known taping units generally comprise a support frame to be inserted in a suitable space of the taping machine, delivery means for the adhesive tape, an entry application roller for the application of the tape on a short vertical part of the leading wall of the case and along the entire bottom or top wall (according as to whether the taping unit is fitted to the bottom or to the top) of the case, an exit application roller for the application of the tape on a short vertical part of the trailing wall of the case and a cutting blade for the separation of the desired length of tape from a continuous roll which may be used for several operations.
The two application rollers move between an extracted or at rest position in which they protrude from the outline of the frame of the taping unit so that they are inserted in the progress path of the case and a retracted position in which the rollers are included completely within the outline of the frame so as to allow the progress of the case itself.
The displacement of the entry application roller from the extracted position to the retracted position is determined by the engagement of the leading wall of the case with the roller itself, which is forced by the above leading wall to move progressively along a retracted path which will allow it to simultaneously apply the adhesive tape to the leading wall of the case. Once retracted, and while the case continues to progress the same entry roller then continues the application of the tape along the bottom or top wall of the case.
The similar movement of the exit application roller can, in turn, be controlled autonomously, but still by the engagement with the progressing case, and it may also be the direct and compulsory consequence of the retraction movement of the entry roller.
The return movement of the two application rollers to the extracted position is subsequently determined by the disengagement of the case from the rollers themselves in combination with the pushing action of suitable elastic means. During such return movement, the exit roller makes the tape adhere to the trailing wall of the case.
Of particular interest is the return movement of the entry application roller, which must occur so as to ensure the correct application of the tape to the leading wall of the case with a suitable passage over the critical point represented by the jointing edge between the above leading wall and the adjacent bottom or top wall, where there are also present the ends of the folded side flaps which ensure the closing of the case and where it is possible that the ends side flap can be turned over. At the same time, the return movement of the entry roller must be such as not to damage the case, in particular, again, at the above edge. In other words, the movement must be executed so that the tape is forced sufficiently firmly against the case, but also so as to avoid resistances greater than those which the case itself may sustain.
A known system for the return of the entry roller provides for the roller to be freely supported in a rotatable way by an arm pivoted on a fixed axis included within the outline of the frame of the taping unit and next to the latter's entry end, so that the roller follows a path of an arc of a circle which is convex towards the outside.
This known system has the disadvantage that, so as not to substantially increase the size of the taping unit, the entry roller support arm is necessarily somewhat short and determines an entry angle of the roller within the outline of the frame, which angle is fairly substantial. This causes an undesirable resistance at the most delicate point of the case, that is at the abovementioned jointing edge between the leading wall and either the bottom or the top wall.
Another known system invented so as to overcome the above disadvantage has the entry application roller mounted on a support arm which is movable along an oblique rectilinear guide so as to follow a rectilinear path with, component in the direction of the progess of the case. This solves the problems related to the resistance and to the entry angle, but makes it inevitable to use a frame of larger dimensions, so as to accommodate the long stroke of the roller retraction. In addition, again as a result of the length of the retraction stroke, the problem is created of accompanying and recovering the tape when the roller performs the roller retraction movement.